Nearly 25 percent of all shopping conversations are posted online by consumers while they are physically inside a store, according to a study released by ListenLogic, a social media intelligence firm. Whether it’s shopping at an electronics retailer or eating at a fast food restaurant, more consumers are posting their opinions via mobile devices while they shop.

“We were shocked a year ago when it was hovering around 15 percent,” says Mark Langsfeld, cofounder and CEO of ListenLogic. “Within the past four or five months—right after the Christmas holidays—restaurants, retailers, and other venues have seen it nearly double.”

The study, “Mobile Social Shoppers,” looked at 16,500 online and social media discussions about the shopping experience in the retail and food service industries during the first quarter of 2011. It found that nearly one in four comments were posted from a mobile device while the consumer was in the store. This was an increase from the year-ago quarter, when nearly one in six comments were made while in the store. Topics of conversation in the more recent study included comparing prices, seeking assistance, checking in, arranging places to meet, and interacting with staff.

While the numbers are staggering, they’re not too unexpected. With more than 200 million smartphones sold within the past six months, it’s no wonder so many social shopping conversations are taking place. “Consumers are using these devices as intended,” says Vincent Schiavone, cofounder and chairman of ListenLogic. “They’re using their iPhone, Android, or BlackBerry devices to post updates, tweets, pictures, and video wherever they go.”

For retailers, this melding by consumers of their online and offline worlds creates not only an opportunity but also an obligation to interact with customers while they are in the store. And they can’t afford to wait. “The big driver is that it’s real time. It can’t be five or 10 minutes later because, by then, the customer is gone,” Langsfeld states. “You need to respond in instantaneous fashion so you can build a relationship with the customer while she’s still in the store.”

Responding properly will require attention to detail by employees, because a frowning customer on a long line at the check-out counter using her smartphone might well be posting a critical comment about the store’s allocation of resources.

It could also require some social media monitoring. A retailer that spots a customer’s online gripe right away can send out a quiet alert to employees that an unhappy customer is in the building, and employees then can turn up the charm a notch, Langsfeld suggests. “Maybe it warrants a visit. Go over and say, ‘Is everything OK here?’ or ‘Is there anything I can do for you today?’”

A simple gesture like that can turn a negative experience into a positive one and create a brand advocate for life, Langsfeld adds. “Today, it’s commonplace for a customer to want a company to care about him, get back to him, and be responsive to his complaints,” he says. “Companies that can do that are seeing positive results right now.”